INCOME TAXES (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current income tax provision
Federal		$ 260,000	$ 295,000	$ 6,086,000
State		1,633,000	1,670,000	2,449,000
Total current income taxes		1,893,000	1,965,000	8,535,000
Deferred income tax provision
Federal		319,551,000	376,728,000	193,974,000
State		41,459,000	68,589,000	9,897,000
Total deferred income taxes		361,010,000	445,317,000	203,871,000
Total provision for income taxes		362,903,000	447,282,000	212,406,000
Income Tax Reconciliation
Income before income taxes		1,517,935,000	1,040,801,000	957,956,000
Less: Net income attributable to noncontrolling interests		3,329,000	205,678,000	391,460,000
Net income attributable to ONEOK before income taxes		$ 1,514,606,000	$ 835,123,000	$ 566,496,000
Federal statutory income tax rate		21.00%	35.00%	35.00%
Provision for federal income taxes		$ 318,067,000	$ 292,293,000	$ 198,274,000
State income taxes, net of federal benefit		38,668,000	16,197,000	12,303,000
Deferred tax rate change, inclusive of valuation allowance		5,552,000	141,283,000	43,000
Other, net		616,000	(2,491,000)	$ 1,786,000
Deferred tax assets
Employee benefits and other accrued liabilities		91,587,000	85,355,000
Federal net operating loss		420,318,000	159,162,000
State net operating loss and benefits		108,004,000	73,277,000
Derivative instruments		22,108,000	30,060,000
Other		13,378,000	13,546,000
Total deferred tax assets		655,395,000	361,400,000
Carryforward expected to expire prior to utilization		(73,820,000)	(66,632,000)
Net deferred tax assets		581,575,000	294,768,000
Deferred tax liabilities
Excess of tax over book depreciation		73,113,000	64,508,000
Investment in partnerships (a)		728,193,000	77,035,000
Regulatory assets		0	15,000
Total deferred tax liabilities		801,306,000	141,558,000
Net deferred tax assets (liabilities)		(219,731,000)
Net deferred tax assets (liabilities)			153,210,000
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount		$ 5,600,000	54,100,000
Deferred Tax Assets, Gross, Noncurrent	$ 2,100,000,000
Deferred Tax Asset, Tax Basis	8,800,000,000
Deferred Tax Asset, Book Basis	$ 3,000,000,000
Excess Tax Benefit from Share-based Compensation, Operating Activities			$ 73,400,000
ONEOK
Income Tax Reconciliation
Federal statutory income tax rate	37.00%